LinuxCNC on non-backdoored hardware - what are the options?

I really don't see using a obsolete CPU is a viable alternative. I know the problems of that chip after using an imagesetter in the printing industry. This was a film recorder capable of 4800 dpi. The demise of that chip series basically obsoleted  the Mac based RIP software driving the device as it was written for that chip set. My experience was before 2005 so why would it be a viable option now?

And what about RPi4?
It works well. Whether with Mesa or with EtherCAT, for example.

And isn't it enough just to get rid of the possibility of communication to the world? Even if there is some coprocessor spying, the information will never leave the PC.

are you designing new boards or using existing?

We'd like to use existing boards.

by 68k you mean 68000 Motorola processors?

Yes, they are non-backdoored and (later chips) are capable, but we'd prefer to use something more modern.

how about using pre 2005 Xeon workstations?

I'll look into this. Do you happen to know the best Intel-based industrial workstation from 2005? Or some idea of the reliable manufacturers who were producing off-the-shelf machines for this purpose around this time? It's hard to determine this through searches.

We're also looking at AMD options, since AMD did not backdoor their CPUs until several years after Intel. I have found a list here of non-backdoored AMD CPUs. Again, however, I am finding it difficult to determine precisely which manufacturers and workstations from this era are advisable to use for industrial applications.

Obviously, I can just build custom systems from these older, secure components. But, I wondered if anyone knew of any good off-the-shelf complete-workstations using these non-backdoored AMD CPUs?

Thanks again for everyone's help on this topic!

And what about RPi4?

Sadly, this solution is also backdoored . We looked into the modern single-board options,like the RPi4, but there appears to be a problem with secure computing across the industry today. The only viable option seems to either air-gap a modern, backdoored, surveillance system CPU, or use a processor manufactured from 2005 or prior (Intel) or 2012 or prior (AMD).

Since we don't want to air-gap, or support surveillance-based CPU manufacturers, it looks like the way forward is to retrace the 'evolution' of computing to the point before CPUs were backdoored, and for us to choose a system that can be trusted.

Thanks for all the suggestions and advice so far.

After more research into this problem today, we have determined that we cannot reliably secure a 'modern' computer. It appears that the entire microprocessor industry has turned their CPUs into surveillance devices. This makes them obsolete for any serious industrial work - if they are connected to the internet.

We have therefore decided to completely air-gap our LinuxCNC manufacturing systems, and to physically remove their networking hardware.

The problem extends beyond the chip-on-chip surveillance processors embedded in AMD and Intel CPUs: We additionally ran into the problem of auditing a version of Linux itself, which is a massive undertaking that we don't have the resources to undertake.

The best solution appears to be to air-gap the Linux computers we use for manufacturing and then use seperate machines running OpenBSD on Libreboot compatible systems for internet comms.

I'm still interested in hearing from others who have addressed this issue, but my conclusion is that air-gapping the manufacturing process is the only way to be sure we are secure.

Arguably Opensource Linux with thousands of users auditing and checking the code would be more secure than OpenBSD with 6-12 security auditors.